The present invention relates to fuel systems for gas turbine engines. More particularly, the present invention relates to a gas turbine engine fuel system having an externally-mounted fuel manifold that is supported to minimize vibrations of the fuel manifold, and that is configured to reduce vibration-induced stresses at connection fittings in the fuel distribution conduits to minimize cyclic-stress-induced cracks in the fuel distribution system adjacent connection fittings.
Gas turbine engines generally have an externally-mounted fuel distribution system that includes a fuel manifold for distributing fuel to a plurality of circumferentially-disposed fuel nozzles. The fuel manifold is often a tubular ring that surrounds the engine and that is supported by brackets that are carried on the engine casing and that space the fuel manifold radially outwardly of the outer surface of the casing. Because the fuel manifold ring is suspended outwardly of the engine casing, it is subjected to vibration when the engine is in operation. Such vibration induces vibratory forces that impart cyclic stresses on various fuel system components, sometimes leading to the formation of fatigue cracks. Such fatigue cracking sometimes occurs adjacent a ferrule that is brazed to a tubular fuel conduit. The ferrule usually has an enlarged end over which a coupling nut is provided to engage with a cooperating fitting to connect the fuel conduit with another element of the fuel system, such as a fuel nozzle.
Cracking of fuel conduits is, of course, undesirable because leakage of fuel around a hot engine surface can result in a fire. Accordingly, fuel supply lines are often shrouded or enclosed, so that any fuel leakage can be contained, collected, and conveyed to a suitable disposable point and thereby avoid a fire hazard. Although such shrouding provides an effective containment mechanism, it is desirable to avoid leakage as much as possible.
One way cracking-induced fuel leakage can be minimized involves reducing the amplitude of vibration of the fuel system components, to minimize the cyclic stresses thereby induced, and thereby minimize the tendency toward cracking at stress concentration points, such as in fuel conduits adjacent ferrules. Another way to minimize cracking and consequent fuel leakage is to attempt to reduce the susceptibility to cracking at or near fitting connection joints
It is an objective of the present invention to reduce such cyclic stresses on fuel distribution system components and thereby minimize vibration-induced cracking.
Briefly stated, in accordance with one aspect of the present invention, a tubular ferrule is provided for receiving a connecting element for connecting a tubular fluid conduit with a component of a fluid-containing system. The ferrule includes a first end having an enlarged head that defines a shoulder for receiving and engaging a surrounding connecting element. An elongated body extends from the first end to a second end, and the second end is adapted to receive an open end of a fluid conduit so that the end of the conduit is axially spaced from the enlarged head. A passageway extends through the ferrule to define a throughbore having a predetermined passageway diameter. The elongated body has an axial length from the shoulder to the second end of a multiple of passageway diameters.
In accordance with another aspect of the present invention, a fuel supply distributor is provided for conveying fuel from a fuel inlet to a plurality of fuel nozzles. The fuel supply distributor includes an outer housing having a fuel inlet and a plurality of fuel outlets. At least one inner conduit is carried within the outer housing and is spaced from an inner surface of the outer housing, wherein the at least one inner conduit extends from the fuel inlet to a fuel outlet. The at least one inner conduit includes an elongated ferrule that carried at an outer end of the fuel conduit. The elongated ferrule has an inner throughbore and a tapered outer surface that extends from an enlarged head end that is adapted to receive a connecting element for connecting the at least one inner conduit to a fluid system having a conduit connection end. The conduit connection end is spaced axially from the enlarged head end.